1. Field of the Invention
The present invention relates to a cleaning apparatus for cleaning both surfaces and the circumference of a magnetic disk or other disk shaped workpiece.
2. Description of the Related Art
FIG. 16 is a plan view of an example of a cleaning apparatus of the prior art, while FIG. 17 is a sectional view along the line A--A of FIG. 16.
This cleaning apparatus is similar to the art described in Japanese Patent Laid-Open No. 62-84971. The outer periphery of a workpiece W is held by three chucks 100. The both surfaces of the workpiece W are cleaned by sponge cleaning pads 110 and 111, while the outer circumference and the inner circumference of the workpiece W are cleaned by rod-shaped brushes 120 and 121.
Specifically, as shown by the solid line in FIG. 18, each of the chucks 100 has a roller 102 rotatably attached to a shaft 101 and holds the outer periphery of the workpiece W by a groove 102a of the roller 102.
Further, the cleaning pads 110 and 111 rotate by being driven in a state gripping the both surfaces of the workpiece W, while the rod-shaped brushes 120 and 121 are rocked up and down while being rotated in a state contacting the outer circumference and the inner circumference of the workpiece W.
By this configuration, when the cleaning pads 110 and 111 are driven to rotate, the workpiece W turns along with this. The rollers 102 are driven to rotate around the shafts 101 so as to allow rotation of the workpiece W. By spraying the workpiece W with cleaning water, not shown, the both surfaces of the workpiece W are cleaned by the cleaning pads 110 and 111. On the other hand, the outer and inner circumferences of the workpiece W are cleaned by the rotation and rocking action of the rod-shaped brushes 120 and 121. All the surfaces of the workpiece W are therefore cleaned by these cleaning pads 110 and 111 and rod-shaped brushes 120 and 121.
There are the following problems with the above cleaning apparatus of the related art, however.
Since the workpiece W is turned along with the rotation of the cleaning pads 110 and 111, the rotational speed of the workpiece W is extremely low. Therefore, a long time is required until the cleaning is completed and the work efficiency is extremely poor.
Further, since the apparatus is structured to hold the outer periphery of the workpiece W by the grooves 102a of the rollers 102, as shown by the broken lines in FIG. 18, the grooves 102a become abraded in a short time and the workpiece W consequently tilts and will no longer move. As a result, it is necessary to stop the cleaning apparatus and frequently replace the rollers 102. This has been a factor lowering the operating rate of the cleaning apparatus.
Further, it was necessary to specially provide the rod-shaped brushes 120 and 121 rotated and rocked by a not shown drive mechanism so as to clean the outer and inner circumferences of the workpiece W. This invited a large size and higher costs in the apparatus.
Further, since the cleaning pads 110 and 111 rotate horizontally with respect to the plane of the workpiece W, the rotational forces of the cleaning pads 110 and 111 act not only in the circumferential direction of the workpiece W, but also the radial direction. The abrasives etc. in the polishing fluid therefore cause scratches in the radial direction of the workpiece W. That is, when the workpiece W is a magnetic disk, as shown in FIG. 19, bit areas B are continuously formed in the longitudinal direction of the track T of the width b.
If a track T is scratched in this way, bit errors will occur and the signal reproduction will be inhibited. If the width a of the scratches C in the longitudinal direction of a track T, that is, the circumferential direction of the workpiece W, is made smaller than 1/4 of the track width b, however, bit errors will not occur. Therefore, scratches of a width of 1/4 of the track width b can be allowed. The size of the abrasives of the polishing fluid etc. is extremely small, and the width a of the scratches caused by the abrasives etc. is smaller than 1/4 of the track width b.
Therefore, there is not that much of a problem even if a scratch is formed in the circumferential direction of the workpiece W. As opposed to this, however, as shown by the broken lines, if a scratch C is formed in the radial direction of the workpiece W, it will cover the majority of the extremely small width bit area B and therefore bit error will occur. Therefore, in cleaning where scratches are formed in the radial direction of the workpiece W like with the above cleaning apparatus of the related art, bit errors frequently occur in the magnetic disk etc. after cleaning. In particular, the bit error was remarkable in cleaning of high density magnetic disks endangering their very usefulness.
Some of the cleaning apparatuses of the related art, however, such as with the cleaning apparatus of Japanese Patent Laid-Open No. 9-69502, drive one of the chucks 100 to rotate to make the workpiece W turn at a high speed and thereby improves the efficiency of the cleaning work. In such an apparatus as well, however, if the roller 102 of the chuck 100 driven to rotate abrades, the frictional coefficient of the portions of contact of the roller 102 and the workpiece W will be reduced and there is the danger of the roller 201 spinning on its own and the workpiece W no longer being turned.